Several methods of remotely determining the location of faults in electrical circuits are known. Such detection may save time and effort in isolating and/or conducting repairs on the relevant part of a circuit by comparison with a physical search for the fault. In particular the conductors may be very long (e.g. overhead power lines), hidden by insulation (an insulated cable having multiple conductors therein) or only inconveniently accessible. Such known location methods are often however dependent on the presence or otherwise of particular components within the circuit and further are often suited only to alternating current circuits rather than direct current circuits. There is an increasing interest in the use of direct current power distribution throughout the power industry. This interest is largely driven by the increased usage and advance of power electronic technologies which have facilitated more interconnected and efficient use of direct current systems. Recently proposed applications for direct current range from large scale multi-terminal systems, such as for offshore grid applications, to smaller scale applications such as microgrids, ships and aircraft.
Some existing fault locating techniques are usable with direct current circuits. They include the use of electrical travelling waves and wavelet analysis. This method is based on the concept that the occurrence of an electrical fault sets up a travelling wave which propagates from the point of fault. Current and voltage travelling waves are related in both time and origin which, using wavelet analysis, allows a fault's location to be determined. Disadvantages of these techniques include their poor detection of nearby faults. Due to very short travel time from nearby faults, the travelling waves cannot be easily distinguished without the use of high measurement speeds and sampling. Furthermore the travelling waves may be damped and reflected by any discontinuities in conductor impedance, making their use less attractive for systems with large inductive filters.
Another fault detection and location approach based on the analysis of travelling waves has been proposed and is better suited to smaller scale systems. Rather than measuring the initial travelling waves resulting from the occurrence of a fault in the system, the proposed approach is based on the injection of current pulses into a network to facilitate fault location and detection. It is the reactions from these injected currents which can be used to determine fault location. Drawbacks of this approach are that an additional indicator is required to trigger this injection of current, limiting its potential for use as a primary protection system.